Materials Science101

Materials Science 101

It's back to school for astronaut
trainees, too

Sept.
15, 1999: You've climbed to the top of the pack, you're a
PhD in astrophysics or a Top Gun pilot, you've just been selected
to be an astronaut. So what's your first task? Go back to school
to become a generalist after studying to be a specialist.

Right: Dr. Sharon Cobb of NASA's Marshall Space Flight
Center examines a model of a crystal lattice. One of the key
points of her lecture is that processing materials in the microgravity
of space reduces defects like the spot, at the center of the
model, where an extra row of atoms has wedged into the lattice.
Links to 600x425-pixel, 96KB
JPG. Or click here for 3024x2252-pixel,
1.2MB JPG. Credit: NASA/Marshall

Because astronauts are called upon to do a little of everything
on the job, their training encompasses far more than how to operate
the Space Shuttle or - with the new candidates in training -
the International Space Station (ISS).

Among the many fields astronauts must know is materials science
in microgravity, one of the principal missions for ISS. Materials
science research aboard the ISS is sponsored by the Microgravity
Research Program at NASA's Marshall Space Flight Center in Huntsville,
Ala. Approximately 60 percent of the planned science experiment
time aboard ISS is devoted to the microgravity sciences and commercial
microgravity investigations.

"This type of training is challenging because the astronauts
have a range of backgrounds from mathematics to materials science,"
said Dr. Sharon Cobb, the project scientist for the Materials
Sciences Research Facility here at NASA/Marshall. Cobb recently
gave an introductory class, including hands-on labs, to the most
recently selected astronaut candidate class at Johnson Space
Center.

"I gave an overview - with
a number of essential details - of what materials science is
and why we want to do this research in microgravity. Later the
astronauts will get more detailed training on specific experiments
as the hardware is developed for flight."

Ironically, part of microgravity materials science
originated with early space station programs. In the 1960s, engineers
at NASA/Marshall and elsewhere wondered what would happen in
space it they tried to weld together large parts of a spacecraft.
Other engineers needed to know how liquid propellants would behave
inside a rocket stage that was coasting between engine firings.

From this came the realization that no one fully understood
what would happen if gravity's effects were removed from materials
that were liquefied, mixed, and resolidified. Early flight experiments
were conducted aboard the last Apollo missions. The discipline
grew and became a major aspect of Skylab's experiments in 1973-74,
and a centerpiece of Space Shuttle and Spacelab missions during
1983-98.

Animated images show the growth
of dendrites, tree-like structures, as a liquid cools in space
(at a rate much faster than actually occurred). While the materials
are transparent organic compounds - succinonitrile (left) and
pivalic acid (right) - their behavior is a close mimic for what
happens at a smaller scale inside opaque molten metals. Credit:
Rensselaer Polytechnic Institute

Cobb reminded the astronaut candidates that advances in materials
science in 1-g make their missions possible, from the new lithium-aluminum
alloy that lightens the Shuttle External Tank so more payload
mass can be carried to orbit, to the urethane-coated nylon pressure
bladder that will keep them in a safe atmosphere during space
walks.

"Manufacturing is 17 percent
- $1.2 trillion - of the U.S. gross domestic product," Cobb
explained. "That means that even modest improvements in
materials and their production can have great economic impact.

For example, the 1998 Metalcasting Industry Technology Roadmap
lists "lack of knowledge of process-microstructure-chemistry-property
interactions [as one of the ] major technology barriers in materials."

"To make substantial advances," Cobb continued,
"materials processing must transition from a historically
trial-and-error art to become a predictable, controllable technology
in the future."

The epitome of the older method is the story of Thomas Edison
perfecting (not inventing) the light bulb by trying everything
as a long-life filament, and then testing virtually every type
of bamboo after he happened upon that. The properties of materials,
especially under various conditions, were just becoming known
to scientists then.

Today scientists work to be more analytical when designing
new materials. But while their knowledge is highly refined, it
is often limited by gravity's effects.

Scientists have reached the point where a material's interactions
with its container may alter sophisticated measurements of a
property, or mask a fundamental phenomenon. For example, unavoidable
convection - where warm, light fluids rise and cold, dense fluids
sink - disturbs the formation of an alloy or electronics crystal
and causes defects.

Gravity is an inescapable factor
in the equations because it's always there - unless you go to
orbit.

Unless you go into orbit. You're still a captive of Earth's
gravity - that's what holds you and the Moon in orbit - but you're
falling continually so the effect is indistinguishable from gravity
being turned off. Tiny residual accelerations remain, so scientists
refer to microgravity, not zero-G.

The net result is that a new range of possibilities now opens
for materials science.

"The goal of materials processing in space is to develop
a better understanding of the relationship between processing,
structure, and properties so that we can reliably predict the
conditions required on Earth to achieve desired materials properties,"
Cobb said.

Equipment for
first Materials Science Research Rack (MSRR-1)

NASA Quench Module Insert is a furnace capable of reaching 1400oC
(iron melts at 1535oC), with a cold end to establish
a controlled temperature gradient. This insert will also allow
rapid freezing of samples up to 8 mm (1/3 inch) in diameter.
This quenching will enable the history of the solidification
of complex alloys to be maintained for subsequent examination.
The information gained will be applied to foundry practices in
industry.

NASA Diffusion Module Insert is a furnace capable of reaching 1600oC,
and able to maintain a constant temperature along a 100 mm (4
inch) length. Controlled gradients can also be obtained. The
furnace will be used to study the speed and mechanisms by which
electrically active elements can be distributed (diffused) through
a molten element such as a semiconductor. These data are important
to the electronics industry and real values cannot be obtained
on the ground because of the influence of gravity driven convection.

ESA Low Gradient Furnace
Module Insert is a furnace
for crystal growth capable of reaching 1600oC. Samples
can be translated at slow and precise rates within a temperature
controlled environment. Magnetic field capabilities, both static
and rotating are available to influence the liquid flow and improve
the properties of the crystalline product.

ESA Solidification Quench
Furnace Module Insert
is a furnace designed primarily for metallurgical experiments
capable of reaching 1600oC, and including a quench
capability. While initially designed to be used for ESA experiments,
these latter two insert modules may be made available for NASA
experimenters.

NASA Advanced Pattern Formation
and Coarsening Research Module
will be an on- orbit replacement for an experiment module sponsored
under NASA's Space Product Development program. It consists of
a low temperature facility with a precisely controlled bath for
in situ observation of the solidification and growth of
transparent model materials that simulate the behavior of metals
and alloys

Microgravity processing benefits

At
right are two different materials that are expected to benefit
from enhanced processing in microgravity. Non-linear optical
polymers (top two pictures) form more uniform fibers when processed
in microgravity (noted as Âľg) than in 1-g on Earth. Nearly
defect-free optical fibers of ZBLAN, a heavy metal glass, were
produced in Âľg instead of the polycrystalline product that
normally results on Earth. The polymers are a candidate for advanced
optical computing. ZBLAN promises much higher data throughput
than conventional silicon-based fibers. A sampling of other beneficiaries
includes:

Isothermal Dendritic Growth
Experiments (IDGE) aboard three U.S. Microgravity Payload missions
have led scientists to revise their models of how metallic crystals
grow based on photographs and videos of crystals growing in transparent
model materials.

An electromagnetic levitation
furnace flown on two Spacelab missions has allowed scientists
to measure, in detail, the physical properties of several metals
without being contaminated by contact with the experiment apparatus,
as would happen on Earth.

Space experiments on one type
of electronic material -cadmium-zinc-tellurium alloy semiconductors
- led to a 200-fold reduction in imperfections and a potential
increase in the number of circuits that can be produced on one
wafer.

Improved understanding how mixtures
coarsen &SHY; how small particles grow into larger particles
- can help in developing improved turbine blades, among other
applications.

The experiments will be conducted in several racks, each 1
meter wide (almost 40 inches) that will be installed aboard ISS
over the next few years. Cobb is the science community's point
of contact for the Materials Sciences Research Facility which
comprises three Materials Science Research Racks. (ISS will also
host facilities for research in fluids, combustion, biotechnology,
and other areas.)

The MSSR-1 will carry a total
of five experiment furnaces from NASA and the European Space
Agency. Candidates for MSSR-2 and -3 include furnaces that would
take half the rack.

"I often get asked why we need so many different furnaces,"
Cobb said. "Well, most of us have several ovens at home
- a toaster oven, a microwave oven, a regular convection oven,
and then four hot eyes on the top of the oven."

In the same manner, it's almost impossible to design one furnace
that would satisfy every experiment, so several furnaces are
designed with special capabilities. Some are isothermal, meaning
that the whole sample is heated and cooled evenly. Some use gradient
heating where the hot zone travels down the length of a sample,
followed by a cool-down zone. Others provide for rapid quench,
like dipping a hot horseshoe in a bucket of water, to freeze
in the history of the liquid for subsequent examination on the
ground.

Blue circle shows the location of
the U.S. Lab module near the center of mass of the completed
International Space Station. It will house experiment gear mounted
in International Standard Payload Racks (ISPR) such as the one
being inspected at right. The racks are designed to hold virtually
everything on ISS, including furnaces and support equipment for
materials science experiments. Top image links to 900x600-pixel,
257K JPG. Credit: NASA

Cobb gave the astronaut candidates a little practice in these
areas with some basic experiments that parallel what is done
in classrooms and in space. In one demonstration, the candidates
grew crystals of succinonitrile, a chemical that forms dendrites,
tree-like crystals, similar to what happens inside metals.

Already, similar experiments aboard the Space Shuttle have
caused scientists to rewrite some basic assumptions about what
happens in that magical instant as a metal turns from liquid
to solid. More advances are expected as the ISS is completed
and becomes an orbiting materials laboratory.